Wind turbines comprise support structures to which a nacelle holding a generator and a hub with rotor blades is mounted. The support structures are most commonly tubular towers tapering in both, in wall thickness and in diameter from tower base to tower top. Large wind turbines comprise, in general, tower sections, e.g. with a length of 32.8 to 98.4 feet (10 to 30 meters), and the complete tower can reach heights of more than 328 feet (100 meters).
Often, the towers are steel towers, but concrete towers, concrete bases with steel upper sections and shell towers, are also used.
Inside of a tower, components like ladders or lifts provide access to the nacelle for carrying out service, maintenance and repair work. Furthermore, a wind turbine tower houses power and signal cables for transmitting electric power and signals from the generator and other wind turbine components to different receivers.
Components such as a ladder, guiding rails or ropes of an elevator as well as cable trays have to be fixed to the tower to avoid excessive movement. For this reason multiple mechanical connections between the tower and these components have to be established. Different fastening techniques and fasteners are used.
It is common practice to provide welded connections between a wind turbine tower and a structural component attached to the tower. Nevertheless, the establishment of welded connections is time-consuming and labor-intensive. Exact measurements have to be carried out to locate the welding positions inside the tower. Furthermore, the welds can reduce the structural strength of the tower.
Besides, it is known to establish threaded non through-going holes in a steel tower, into which a bolt can be screwed. However, a sharp tool is needed to thread the holes and during the threading process, small cracks can emerge which under mechanical loads, can extend and decrease the stability of the wind turbine tower.